The marked recent increase in overweight and obesity prevalence implicates behavioral factors in the etiology of these problems and, as a consequence, suggests strategies for intervention. The present proposal hypothesizes the trend is attributable, in part, to increasing consumption of energy-yielding beverages since their consumption has risen in concert with BMI trends, their inclusion or exclusion from diets leads to predictable weight changes, they now contribute over 20% of daily energy in the population and they elicit weaker appetitive and dietary responses than semi-solid or solid foods. Four human studies are proposed to contrast an array of appetitive and physiological responses to selected pre-ingestive (e.g., cognitive, orosensory, masticatory) influences on ingestion of fluid and solid food forms. Early work indicated the expected energy content of foods better predicted their impact on appetite than their true energy content and rheological properties influence this expectation. Study 1 will explore the anticipated satiety effects, GI transit time, gut hormone secretion and glycemic response to ingestion of matched fluid and solid food forms by manipulating the expected and actual rheological properties of the foods prior to and following ingestion. A heirarchy of appetitive effects have been reported for the macronutrients, but appear less predictable in fluids. Study 2 will monitor appetitive responses to fluid and solid foods varying in nutrient content to clarify this issue. Because of hypothesized independent and synergistic effects of mastication on appetite, GI transit, gut hormone secretion and glycemic responses, these outcomes will be measured following controlled masticatory activity in conjunction with drinking. Study 4 will examine the role of cephalic phase responses on post-prandial glucose, insulin and selected gut peptide concentrations using fluid and solid dietary stimuli. In addition, the role of learning in these responses will be tested. Increasing evidence suggests that the reward system may override homeostatic appetitive cues in the regulation of feeding. All trials will contrast findings from lean and obese individuals to determine whether the regulatory mechanisms for energy balance may be less precise, especially for beverages, in the latter group. The findings should aid development of dietary recommendations and products to address the problems of overweight/obesity.